The head of the United Nations refugee agency warned Tuesday that Syria could be on the "verge of the abyss" as aid workers brace for a likely increase in the nearly 2 million refugees who have already fled the country's civil war.

For much of the past seven years, Khalid Zir and his family called a makeshift tin shack in the east Jerusalem neighborhood of Silwan home. But now that Israeli authorities have demolished the hut, Zir has become even more desperate.

In every corner of the Egyptian capital, a bustling city of 18 million that rarely sleeps, people are locked up in their homes at night under a military-imposed curfew that has driven people up the walls, sometimes literally.